That seems a fairly high dose of BAP - you may have overdone it.

The alternative answer is that the BAP was not taken up by the seed

l dissolved 0.1 grams in 2 mls  1 molar sodium hydroxide then added water to a final volume on one litre,  actually germination is being inhibited

Tobacco has a light requirement for germination.  Also I have found GA-3 to be much more effective for germination then BAP.  I do not know if BAP will overcome the light requirement.  Also many Solanaceae have germination inhibitors present.  Often it is extremely helpful to soak the seed in a ~25-50% isopropanol or ethanol solution for a an hour-overnight depending on the size of the seed and the amount of inhibitors present.  The reason for this treatment is that it aids in leaching out at least some of the germination inhibitors.  With Nicotiana I have left the seeds overnight and not had any problems.  As the seeds are extremely small it is often helpful to do this in a petri dish on a filter paper, or make a small envelope of filter paper and place the seeds inside prior to treatment.  The reason for this is that the seeds become very difficult to handle when wet and like sticking to everything they touch. 

Thank you Dave wanted to understand the physiological explanation for seed inhibition by BAP . Tobacco seed doesnt have any germination inhibitors its the non deep physiological dormancy that does resitrict germination. I basically doing  work in seed physiology covering phyto hormones responses (GA- AND BAP), water and hydrogen peroxide response during seeed after-ripening incubated in diffrent light and temperature regimes. The BAP non responnse is really an intresting angle that will help us understand the hormonal responses during seed germination .